This invention relates to an electromagnetic lifting device for handling a ferromagnetic material, and more particularly to the device of the type described, which is adapted for use in safely handling the ferromagnetic material having a curved surface or irregular surface, or the ferromagnetic material susceptible to deflection.
In using an electromagnet for lifting a worked or unworked ferromagnetic material having a concave or convex surface, it is imperative that the contacting area between the attracting surface of the electromagnet and the surface of the ferromagnetic material to be lifted be increased so as to exert an effective magnetic force on the material.
Hitherto, it has been a common practice to use a large size electromagnet, as compared with the size of a ferromagnetic material to be lifted, in handling the material like a steel product having a curved surface or the material like a metal sheet or plate having a wide width and susceptible to deflection, in the field of steel-stock working industries, such as iron works and shipbuilding yard. More particularly, the conventional electromagnetic lifting device suffers from disadvantages in that there may not be achieved a sufficient contacting area between the flat surface of a single magnetic pole of an electromagnet and the curved surface of the steel product, and that there may not be maintained a sufficient contacting area between the flat pole surface and the metal sheet or plate due to the deflection of the cantilever portion of the sheet or plate. This brings about a danger of the material dropping off the magnet when handling same, thereby necessitating the use of a large size electromagnet.
For avoiding said shortcomings, there have been proposed attempts such as disclosed in the Japanese Utility Model Public Disclosure No. 80052/1973 and the Japanese Utility Model Publication No. 16363/1972. According to these proposals, there are provided magnetic poles which are accommodated to the curved surface of a steel product by providing a deformable bag containing ferromagnetic powder therein or a flexible ferromagnetic material which is secured to an electromagnet, in an attempt to increase the contacting area between the magnetic pole and the steel product. However, those attempts pose problems such as poor durability and a reduced magnetic force.